Why Too Much HIIT Might Be Harming You!

Is this popular approach to exercise really the right way to go..?

In the world of fitness, HIIT (High Intensity Interval Training) has gone mainstream. If you are unfamiliar with it, it is the type of training that leaves you laying in a pool of sweat with burning lungs and heavy muscles. I’m referring to metabolically demanding intervals/circuits that are performed at a high intensity for short to medium length intervals, followed by a short rest period – this is then repeated. We might refer to this as glycolytic training.

There are clear benefits to this type of training (such as improved cardiovascular fitness and time efficiency), however, the issue with performing this kind of training day in day out is that performance will soon plateau and the body will pay a price. Even for athletes, glycolytic training is usually reserved for the final 8 weeks of their peaking cycle.

So what does glycolytic mean? To answer this, let’s have a brief rundown of how our energy systems work….

The energy currency we use is called ATP (Adenosine Triphosphate). This is what our muscles need to power movement. The body is supplied with ATP by three different energy systems:

1) Creatine Phosphate system (CP) – lasts 10 to 15 seconds (anaerobic)

2) Glycolysis – up to 2 minutes (anaerobic)

3) Oxidative system – > 2 minutes (aerobic)

There is a complex interaction between all 3 systems since all 3 run alongside each other, but the crux of it is this…. If you start sprinting, the first 10 – 15 seconds of ATP will be supplied by the CP system. This is a powerful system but the ATP is used quickly. If you continue to ‘sprint’, at about 20 seconds, the body has to slow down because it has now switched to glycolysis. This system isn’t as powerful as CP and can’t supply ATP as quickly, but it supplies ATP for up to 2 minutes. Finally, after about 2 minutes glycolysis take its toll and the oxidative/aerobic system kicks in to provide any further ATP – this oxidative system can last forever (potentially) and it’s likely that the body parts will give up before the oxidative system runs out. You’ve guessed it though; the trade-off is that once the process becomes aerobic then power is reduced once again. You are no longer sprinting, and have started jogging or walking (you get the gist).

If you think about it this way, the glycolytic system is sandwiched in between the CP and the aerobic energy systems. It is neither the most powerful nor the most efficient. It also comes at a cost. The by-product of glycolysis is metabolic waste – the muscles become more acidic (acidosis – due to increased H+ ions) and cells are damaged. This explains the immediate feelings of heavy muscles and nausea following glycolytic training. The only way the body can recover from this is by utilizing the oxidative system to replenish ATP – the response will be to pant and suck up air to give the body all the oxygen it needs to reproduce ATP. So, if you have a well-developed aerobic system, you will recover much quicker.

So what does all this mean? In moderation glycolytic training has its place, however, an over reliance on it for the general fitness enthusiast is likely causing more harm than good. The effects of acidosis are still being studied and they may not become evident until the long term, but we know sustained cell damage is undesirable. What is apparent is that it is unlikely to be the optimal way to train most of the time – the CP system is more powerful (you run faster, jump higher) and the oxidative system is more efficient (and lasts forever) and has no nasty side effects.

So if you are feeling run down, constantly fatigued, starting to pick up injuries or have lost your mojo, then it might be worth considering whether you are leaning too much on glycolytic training.

In a future article, we can look at an alternative training protocol for staying fit (hint – it involves CP and Oxidation, but not glycolysis).

Stay Bulletproof,

Coach Craig.

Author - Craig Peterson - Personal Trainer & Mentor

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